In conventional commercial systems, at least two solenoid valves are used to control a single-acting cylinder, and at least three solenoid valves (see, e.g., U.S. Pat. No. 8,096,568 B2 to Huth) or four solenoid valves (see, e.g., U.S. Patent Application Publication No. US2005/0050886 A1 to Bauer et al.) are used to control a double-acting system independently at the same time. In other known systems, three solenoid valves in combination with one proportional pressure-reducing valve are used to control a double-acting system independently at the same time (see, e.g., U.S. Pat. No. 7,219,779 B2 to Wolfgang and U.S. Pat. No. 7,048,280 B2 to Brandenburger). Another known system uses two proportional and two solenoid valves to control a double-acting system independently (see, e.g., U.S. Pat. No. 7,753,385 B2 to Bitter).
Some existing systems are equipped with additional, non-integral check valves for load sensing/piloting. Additionally, check valves or low-leakage solenoid-operated valves are included in some conventional systems to hold the mechanical system rigid when power is not applied.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some aspects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.